JPH09221367A - Conductive silicon carbide material composite material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a SiC material composite material high in tenacity by mixing carbon or a carbon-containing compd. to a powdery mixture of the SiC and the one of more than one kind among a boride of Ti, Zr, Nb, Ta, Cr and Mo and burning the mixture. SOLUTION: 0.5-10 pts.wt. (expressed in terms of carbon in weight) carbon or carbon-containing compd. such as phenol is added and mixed to 100 pts.wt. powdery mixture of 60-95vol% SiC powder having about <=3μm grain size and 5-40vol% boride more than one kind among TiB2 , ZrB2 , NbB2 , TaB2 , CrB and MoB and having about <=30μm grain size. This mixture is compacted, burned at about 1900-2300 deg.C for about 15-60min in an inert gas atmosphere such as argon, then, the burned mater is cooled to room temp. by a speed of about 50 deg.C/min, and a conductive SiC material composite material being a sintered body in which the boride is dispersed in a continuous SiC substrate and the carbon having a graphite structure is present in an intercrystalline phase is obtained. And the material is subjected to HIP treatment at about 1800-2000 deg.C and about 100-2000atm pressure in an Ar gas atmosphere and the sintered body having about >=95% relative denseness is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive silicon carbide based composite material having high toughness and high strength and capable of varying resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Silicon carbide, which has excellent strength and oxidation resistance especially at high temperature among ceramic materials, has attracted attention as a high temperature structural material used in relatively harsh environments such as automobile engines and gas turbines. Came. However, its electrical resistance is as high as 10 ⁴ Ω · cm, and since it has almost no electrical conductivity, it is not possible to perform electrical discharge machining that is inexpensive and highly productive, and the production cost as a machined part is considerably high. Among the ceramic-based materials, the toughness is considerably low, and this brittleness is a major obstacle to practical application. On the other hand, although metal materials have electrical conductivity, they can be subjected to electrical discharge machining, but they are considerably inferior to ceramic materials such as silicon carbide in terms of high temperature strength and oxidation resistance, and the selection of the electrical resistance value that the material can develop is extremely limited. It could only be realized within the specified range. Therefore, for example, 1
There has been a demand for a conductive material having mechanical characteristics that can be stably used even in an oxidizing atmosphere at a high temperature exceeding 000 ° C.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to have a high temperature strength and an oxidation resistance which cannot be obtained with a metal material, and to show a toughness value higher than that of a silicon carbide sintered body, and a normal metal material. An object of the present invention is to provide a conductive material capable of giving arbitrary electric conductivity from a wider range of electric conductivity and a method for producing the same.

[0004]

Therefore, as a result of various researches conducted by the present inventors, titanium, zirconium, niobium, tantalum, which has conductivity in silicon carbide and is chemically stable,
Excellent by forming particles of one or more selected from the group of borides of chromium and molybdenum and dispersing at least carbon having a graphite structure at the grain boundary to obtain a composite sintered body. It has been found that it has high toughness and high temperature strength and has high electrical conductivity, and its electrical conductivity can be changed in a relatively fine order from a wider resistance value range than general metal materials. The present invention has been completed.

That is, according to the present invention, 60 to 95% by volume of silicon carbide is used.
And 100 parts by weight of a mixed powder containing 5 to 40% by volume of any one or more of boride of titanium, zirconium, niobium, tantalum, chromium, and molybdenum, carbon or a compound containing carbon is 0.5 in terms of carbon weight. Sintered mixture of 10 to 10 parts by weight, wherein the boride phase is dispersed in a continuous silicon carbide base phase, and at least carbon having a graphite structure is present in the grain boundary phase. Is a conductive silicon carbide composite material.

The present invention also provides a silicon carbide of 60 to 95% by volume.
And 100 parts by weight of a mixed powder containing 5 to 40% by volume of any one or more of boride of titanium, zirconium, niobium, tantalum, chromium, and molybdenum, carbon or a compound containing carbon is 0.5 in terms of carbon weight. A mixture obtained by adding 10 parts by weight to 10 parts by weight is sintered at 1900 to 2300 ° C. and cooled at a cooling rate of about 50 ° C./min or less from the sintering temperature in a continuous silicon carbide base phase. Is a sintered body in which the boride phase is dispersed in and a carbon having a graphite structure is present in the grain boundary phase.

Further, the present invention is a method for producing a conductive silicon carbide based composite material, wherein the sintering is pressure sintering.

In the present invention, the conductive silicon carbide composite material produced by any one of the above production methods is not encapsulated but an inert gas is used as a pressure medium, the pressure is 1000 atm or more, and the temperature is 1800 to 8000. It is a method for producing a conductive silicon carbide based composite material, which is characterized in that HIP treatment is performed at 2000 ° C.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Silicon carbide used as a raw material in the present invention is preferably a powder having a particle size of 3 μm or less from the viewpoints of sinterability and improvement of the strength of a sintered body, and its crystal structure is either α type or β type. However, it is preferable that the β type is relatively easy to sinter. Further, for the purpose of improving the sinterability, it is also possible to use a silicon carbide powder to which metal aluminum or aluminum oxide, which is a known sintering aid, is added in an amount of about 0.5 to 3% by weight. It is desirable to avoid mixing because it may lead to deterioration of properties at high temperature and may affect electric resistance. In particular, since powdery silicon carbide easily forms silicon dioxide on the surface in the air, it is desirable to use one that has been cleaned with hydrofluoric acid or the like in advance to remove the silicon dioxide on the powder surface. The blending amount of this silicon carbide with respect to the raw material powder mixture is 60 to 95% by volume. When using silicon carbide added with a sintering aid of metallic aluminum or aluminum oxide, the content of silicon carbide containing the aid is set.

The borides of titanium, zirconium, niobium, tantalum, chromium and molybdenum used as raw materials in the present invention may have a purity of approximately 95% or more, and the particle size thereof is more preferably 30 μm or less at the maximum. It is desirable for imparting strength and toughness to the sintered body. The compounding amount of the powder mixture is 5 to 40% by volume of any one or more of the above boride. If the blending amount is less than 5% by volume, the compounding effect becomes poor and the toughness is hardly expected to be improved, and if it exceeds 40% by volume, the oxidation resistance at high temperature is deteriorated, which is not preferable.

In the present invention, carbon or a compound containing carbon is further added to 100 parts by weight of a raw material mixed powder containing silicon carbide and one or more kinds of borides of titanium, zirconium, niobium, tantalum, chromium and molybdenum. It is added in an amount of 0.5 to 10 parts by weight in terms of carbon weight. The carbon to be added here is preferably carbon powder having a crystalline graphite structure, but carbon powder such as carbon black can also be used. Further, instead of directly using the carbon powder, a compound containing carbon capable of decomposing / decomposing components other than carbon in the heating stage may be used as a carbon source.
Examples of such a compound containing carbon include phenol or its resin, tar, and furan resin. If the addition amount is less than 0.5 parts by weight, it becomes difficult to finely adjust the electric resistance and it becomes difficult to densify it, and if it is 10 parts by weight or more, the mechanical properties are deteriorated.

The conductive silicon carbide-based composite material of the present invention is any one of the above-mentioned silicon carbide and titanium, zirconium, niobium, tantalum, chromium or molybdenum boride.
Mixing one or more species and carbon or a compound containing carbon,
The mixture is sintered. This sintered body is dense and is made of silicon carbide in a state in which particles of at least one kind of boride of titanium, zirconium, niobium, tantalum, chromium, and molybdenum are dispersed substantially uniformly and discontinuously. It is firmly held in a continuous base material phase, and further carbon of a graphite structure is generally precipitated in a grain size of about several tens to 100 nm in a grain boundary phase between silicon carbide and a metal boride which is a conductive substance.
In particular, at the triple points of the grain boundaries, carbon re-precipitated by dissolution in silicon carbide is present in the order of several μm. Such a grain boundary portion may contain at least amorphous carbon in addition to crystalline carbon having a graphite structure. The conductive property of this composite material can be adjusted to a desired resistance value by the blending amount of metal boride and carbon, and the range is approximately 1 × 10 ³ to 10 ⁶ Ω · cm.

Next, details of the manufacturing method according to the present invention will be described.
A mixture of the raw materials and the amount thereof is determined as described above, for example, by wet mixing using a solvent such as lower alcohol or water, acetone in a ball mill, and after dried granules by spray drying or the like, if necessary, Mold into the desired shape. The molding may be carried out by any molding method as long as it is a method capable of obtaining a relatively high-density molded body such as mold molding or cold isostatic pressing (CIP). Next, the compact is sintered. Sintering is performed at a temperature of about 1900 ° C. in an inert gas atmosphere such as argon or helium using a heating device capable of adjusting the atmosphere.
Heat at 2300 ° C for about 15-60 minutes. A dense conductive silicon carbide composite material can be obtained by cooling in the furnace after heating or cooling at least 1500 ° C. at a cooling rate of about 50 ° C./min or less, more preferably near room temperature. When a compound containing carbon is used as the carbon source, it is preferable to use an inert gas flow in order to smoothly decompose and remove the non-carbon component. The temperature is 19
If it is less than 00 ° C., it is not preferable because sintering is difficult to proceed and carbon having a graphite structure is not generated. On the other hand, if the temperature exceeds 2300 ° C., it will be over-sintered and the mechanical properties will deteriorate, which is not preferable. If the cooling rate after heating the sintered body exceeds about 50 ° C./minute, carbon having a graphite structure is less likely to deposit, which is not preferable.

In the production method of the present invention, the pressure during sintering can be atmospheric pressure, that is, about 1 atm, but a conductive silicon carbide composite material having higher strength and higher density can be obtained. For this, pressure sintering is preferably performed. Examples of such a pressure sintering method include a known hot pressing method and a method of sintering a material to be fired enclosed in a capsule such as glass by hot isostatic pressing (capsule HIP method). it can.

As for the sintered body having a relative density of about 95% or more, which has been subjected to normal pressure or pressure sintering as described above,
In order to obtain a more dense and more uniform property, the element body is directly enclosed in an argon pressure medium at a temperature of about 1800 ° C to 2000 ° C and a pressure of 10 without being enclosed in a capsule such as glass.
It is also possible to perform HIP processing at 00 to 2000 atm, that is, capsule-free HIP processing. If the HIP treatment temperature exceeds 2000 ° C., grain growth leading to a decrease in strength is observed, and if the HIP treatment temperature is less than 1800 ° C., the effect of the HIP treatment is hardly seen, which is not preferable. Similarly, if the pressure is less than 1000 atm, the effect of HIP treatment is hardly seen, which is not preferable.

[0016]

The metal boride particles such as zirconium boride constituting the present conductive silicon carbide composite material are uniformly dispersed in the silicon carbide matrix to give higher electric conductivity than general metal materials and The toughness value of the material can be significantly improved by the principle of particle dispersion strengthening. Further, carbon in the conductive silicon carbide composite material of the present invention exists mainly in two forms, a so-called amorphous state and a graphite crystal structure, and the former acts as a sintering aid and contributes to the sintering of the silicon carbide base material. . On the other hand, in the latter, the resistance value of the metal boride greatly changes in accordance with a slight change in the compounding amount thereof, whereas the change in the resistance value in accordance with the change of the compounding amount is fairly gradual. As described above, carbon has a resistance adjusting function different from that of the metal boride, and therefore, the conductive silicon carbide composite material boride of the present invention has a desired resistance value in a resistance range wider than that of the metal. Although it can be done, it is possible to manufacture a product in which the value is relatively strictly adjusted to a fine order.

[0017]

【Example】

Example 1 β-type silicon carbide (SiC) having an average particle size of 0.5 μm, which was previously washed with hydrofluoric acid, titanium boride (TiB ₂ ) having a particle size of 4 μm or less and a central particle size of 2.8 μm, Zirconium boride (ZrB ₂ ) with a particle size of 5 μm or less and a center particle size of 2.1 μm, and center particle size of 2.3 μ with a particle size of 5 μm or less
m niobium boride (NbB ₂ ), tantalum boride (TaB ₂ ) having a central particle size of 2.2 μm and a particle size of 5 μm or less, and a particle size of 4 μm
Molybdenum boride (Mo having a central particle diameter of 3.0 μm or less
B), chromium boride (CrB) having a particle size of 4 μm or less and a central particle size of 2.9 μm, and phenol (C ₆ H ₅ OH) were prepared by ball mill mixing at a compounding ratio shown in Table 1. . The mixture was molded by die molding, and each molded body was sintered at 2200 ° C. for 20 minutes in an argon stream adjusted to about 1.0 to 1.1 atm using an electric furnace, It was cooled to about 300 ° C. at a cooling rate of 15 ° C./minute, and then allowed to cool to about 25 ° C. in the furnace to produce dense sintered bodies (invention products 1 to 12).

[0018]

[Table 1]

The obtained sintered body had a bending strength (MPa) in the atmosphere at room temperature (about 25 ° C.) and 1000 ° C., a fracture toughness at room temperature (MPa · m ^1/2 ), and a relative density (%). ), And the electrical resistance (Ω · cm) at room temperature were measured. The values are shown together in Table 1. The bending strength is JIS-R1601.
The three-point bending strength and fracture toughness according to
SEPB method based on S-R1607, relative density was measured by Archimedes method, and electrical resistance was measured by four-terminal method. Further, when the crystal phase was examined by X-ray diffraction and Raman spectroscopic analysis, it was found that any of the sintered bodies was TiB ₂ , ZrB ₂ , NbB.
Any one of ₂ , TaB ₂ , MoB, CrB and β-type SiC
And confirmed the presence of graphite-type carbon.

Example 2 1.29 kg of β-type silicon carbide having an average particle size of 0.5 μm, which had been preliminarily washed with hydrofluoric acid,
A mixture of 0.40 Kg of zirconium boride and 0.063 Kg of carbon black having a particle size of 5 μm or less and a central particle size of 2.1 μm was prepared by ball mill mixing, and this was die-molded to produce a molded body. The molded body was fired under the conditions shown in Table 2 by an electric furnace in the same argon stream atmosphere as in Example 1 above, a hot press furnace in an argon atmosphere, or a capsule HIP method using a HIP device using an argon pressure medium. Tied, 50 ℃ / from the maximum sintering temperature
It is cooled to about 300 ° C. at a cooling rate of 1 minute and then left to cool to room temperature in the furnace to obtain a dense sintered body (invention products 13 to 1).
6) was produced. The obtained sintered body was bent in the same manner as in Example 1 at room temperature (about 25 ° C.) and 1000 ° C. in air, the fracture toughness at room temperature, the relative density, and the electrical conductivity at room temperature. The resistance was measured. The values are shown in Table 2 together. When the crystal phase was examined by X-ray diffraction and Raman spectroscopic analysis, the presence of ZrB ₂ , β-type SiC and graphite-type carbon was confirmed in all the sintered bodies.

[0021]

[Table 2]

[Example 3] The sintered body of the product 13 of the present invention produced in Example 2 was directly placed in a HIP device without encapsulation, and 1000 atm with an argon pressure medium by a capsule-free HIP method. HIP treatment was performed at 1800 ° C. for 30 minutes, and cooling was performed under the same conditions as in Example 1 above.
The respective characteristic values of the obtained sintered body measured by the same method as in Example 1 were as follows: bending strength in normal temperature air was 680 MPa, and 1
The bending strength in the atmosphere at 000 ° C was 660 MPa, the relative density was 99%, the fracture toughness at room temperature was 4.7 MPa · m ^1/2 , the electric resistance at room temperature was 3.1 × 10 ² Ω · cm, which was excellent. It showed toughness and conductivity. The Examination of the crystal phase of the sintered body by X-ray diffraction and Raman spectroscopy, and ZrB ₂ beta
The existence of type SiC and graphite type carbon was confirmed.

[Comparative Example 1] 3.08 kg of β-type silicon carbide having an average particle size of 0.5 μm, which was previously washed with hydrofluoric acid,
A mixture of 0.24 Kg of zirconium boride and 0.06 Kg of carbon black having a particle size of 5 μm or less and a central particle size of 2.1 μm was prepared by ball mill mixing, and this was die-molded to prepare a molded body. A sintered body was produced from the molded body under the same sintering and cooling conditions as in Example 1. The respective characteristic values of the obtained sintered body measured by the same method as in Example 1 were as follows: bending strength of 420 MPa in normal temperature air, 1
Bending strength in atmospheric air at 000 ° C 400 MPa, relative density 96%, fracture toughness at room temperature 3.9 MPa · m ^1/2, electrical resistance at room temperature 20000 Ω · cm, high electrical resistance, poor conductivity. It became a thing.

[Comparative Example 2] 2.56 kg of β-type silicon carbide having an average particle size of 0.5 μm, which was previously washed with hydrofluoric acid,
A mixture of 1.21 kg of zirconium boride and 0.004 kg of carbon black having a particle diameter of 5 μm or less and a central particle diameter of 2.1 μm was prepared by ball mill mixing, and this was molded into a mold to prepare a molded body. A sintered body was produced from the molded body under the same sintering and cooling conditions as in Example 1. The characteristic values of the obtained sintered body, which were measured by the same method as in Example 1, were 210 MPa in bending strength in a normal temperature atmosphere and 91% in relative density, and were extremely poor in compactness.

[0025]

The conductive silicon carbide composite material of the present invention is
The toughness of silicon carbide is greatly improved, and it is possible to stably exhibit relatively excellent mechanical properties even at high temperatures.
It also has good electrical conductivity. This electric conductivity can be produced with high accuracy by the manufacturing method of the present invention, which has an arbitrary electric conductivity within a wider electric conductivity range than a metal material. Due to such characteristics, the composite material of the present invention may be sufficiently used not only as a structural member but also as a functional material such as a resistor, an electric fuse, and a temperature sensor that generate relatively high heat. .

Claims (4)

[Claims] 1. 60 to 95% by volume of silicon carbide and titanium,
0.5 to 10 parts by weight of carbon or a compound containing carbon in terms of carbon weight in 100 parts by weight of mixed powder containing 5 to 40% by volume of any one or more of borides of zirconium, niobium, tantalum, chromium and molybdenum. A sintered body obtained by sintering the mixture to be added, wherein the boride phase is dispersed in a continuous silicon carbide base phase, and carbon having a graphite structure is present in the grain boundary phase. And a conductive silicon carbide composite material. 2. 60 to 95% by volume of silicon carbide and titanium,
0.5 to 10 parts by weight of carbon or a compound containing carbon in terms of carbon weight in 100 parts by weight of mixed powder containing 5 to 40% by volume of any one or more of borides of zirconium, niobium, tantalum, chromium and molybdenum. Add 1 mixture
What is obtained by sintering at 900 to 2300 ° C., and cooling it from the sintering temperature at a cooling rate of about 50 ° C./minute or less, wherein the boride phase is dispersed in a continuous silicon carbide base phase, A method for producing a conductive silicon carbide based composite material, which is a sintered body having graphite structure carbon in the grain boundary phase. 3. The method for producing a conductive silicon carbide based composite material according to claim 2, wherein the sintering is pressure sintering. 4. The conductive silicon carbide composite material produced by the method according to claim 2 or 3, without encapsulation, using an inert gas as a pressure medium, a pressure of 1000 atm or more, and a temperature of 1800 to 8000. A method for producing a conductive silicon carbide based composite material, which comprises performing HIP treatment at 2000 ° C.